The present invention relates to dashpots and related dampening devices, and more particularly to such devices in which some forgiveness is provided for a limited misalignment between the axis of the reciprocating motion to be damped and the axis of the cylinder.
Damping dashpot and related piston-cylinder dampening assemblies comprise a hollow cylinder substantially closed at one end thereof, piston means disposed in and slidable along the cylinder, and a piston rod having a first end portion operatively connected to the piston means for moving the piston means back and forth along the cylinder axis and a second portion extending out of the open end of the cylinder and adapted for connection with a member undergoing reciprocating motion. The piston means in some instances comprises a piston having an outer sidewall snugly fitting within the cylinder inner sidewall so as to preclude the passage of fluid therebetween. The piston means in other instances comprises a piston having an outer sidewall inwardly spaced from the cylinder inner sidewall and fluid blocking means secured to the piston for movement therewith. The fluid blocking means includes a resiliently flexible portion disposed intermediate opposed sidewall portions of the piston and cylinder, respectively, and effective to block passage of fluid therebetween as long as the piston and cylinder axes are substantially parallel. In the latter instances the necessity of maintaining a fluid-tight seal between the piston means and the cylinder dictates that the piston outer sidewall be of sufficient length and in sufficient proximity to the cylinder inner sidewall to maintain the cylinder and piston axes substantially parallel.
Optimally the member to be damped undergoes reciprocating motion along an axis exactly aligned with the axis of the cylinder. However, in practice there is often a degree of misalignment between the reciprocating motion axis and the cylinder axis. To forgive such misalignment, assemblies have been provided in which the piston rod is capable of a degree of pivotal movement relative to the piston, this being accomplished conventionally by means of hinge or universal joint connections between the piston and piston rod, as disclosed in U.S. Pat. Nos. 3,175,646 (issued Mar. 30, 1965); 3,854,557 (issued Dec. 17, 1974); and U.S. patent application Ser. No. 498,585 (filed Aug. 19, 1974), now U.S. Pat. No. 3,939,947 (issued Feb. 24, 1976).
While it is generally recognized that the universal joint piston-piston rod connection represents an improvement over the prior art hinge type connection, it has not proven to be entirely satisfactory. The complex nature of such a connection not only increases both material and production costs, but simultaneously increases the possibility of defective products being produced. Furthermore, the trapping of the end segment of the piston rod within the piston severely limits the degree of free play which the piston rod is able to undergo relative to the piston.
Accordingly, it is an object of the present invention to provide a dashpot capable of forgiving limited misalignment of the axis of the cylinder and the axis of the reciprocating member using a rigid connection between the piston and piston rod.
It is a further object to provide such a dashpot without incurring the increased manufacturing cost and the limitations on free movement inherent in non-rigid piston-piston rod connections.
It is another object to provide such a dashpot which is of simple construction, easy to manufacture, and of suitable longevity.